The Federal Food and Drug Administration (FDA) in the United States has ordered new warnings of the potential health hazards in taking sleeping pills.

The FDA is warning that the popular sleep aids can cause severe allergic reactions and unusual activity while 'asleep' - everything from cooking meals to making phone calls.

In the US more than 45 (m) million prescriptions for such pills were written in 2005.

But some people taking sleeping pills reportedly engage in 'sleep driving.'

That's what Carrie Paps claims she engaged in after taking an Ambien pill, shortly before going to bed one night. When Paps woke up, she claims she was sitting at her desk.

Similar stories have been documented in police reports and lawsuits over the past year.

Doctor Michael Cramer-Bornemann of the Minnesota Regional Sleep Centre said "these are significant behaviours that are not without risk not just to the individual but to the general public, as soon as this gets out of the house and someone is sleep driving, the public is now in danger."

Now the FDA will require the makers of Lunesta, Ambien and eleven other sleep medications to clearly list these possible side-effects on their labels.

The bizarre side effect of "sleep driving" first made headlines when US Representative Patrick Kennedy crashed his car after taking such a medication.